From the NFL and NBA to soccer, tennis, golf, track and field, and more, we selected the 31 athletes who stake a claim as the best in the world at what they do.

Men's soccer: Cristiano Ronaldo

Real Madrid forward

Age: 30

Ronaldo took home the Ballon D'or in 2014 and carried Portugal to the World Cup despite being knocked out in the first round. He has 18 goals in 2015 and 50 goals in 47 games for the 2014-15 season.

Women's soccer: Nadine Kessler

German national team midfielder

Age: 27

Kessler won 2014 FIFA's women's player of the year and was leading a German team that's one of the favorites going into the 2015 Women's World Cup. In October she hurt her knee and will now miss the World Cup.